The reproductive system influences the lifespan of the nematode C. elegans. The germ cells exert a negative effect on longevity, as revealed by experiments in which the germline was removed by laser ablation (1). These animals, which still contain an intact somatic gonad, live 60 percent longer than unablated controls. This phenotype is dependent on the presence of the somatic gonad; therefore, we infer that the somatic gonad signals to promote longevity. These and other findings suggest that the adult animal must interpret counteracting signals from the reproductive system in order to properly regulate its lifespan. The actions of multiple genes are required for this regulation to occur. Specifically, the lifespan extension of germline-ablated animals is dependent on daf-16, a FOXO family transcription factor, daf-12, a nuclear hormone receptor, and daf-9, a cytochrome P450 (1,2). The germline therefore appears to reduce lifespan through regulation of transcriptional outputs and steroid hormone signaling. However, extension of lifespan by germline ablation appears to be independent of the DAF-2 insulin/IGF-1 receptor: long-lived daf-2 mutants live even longer when the germline is removed. This is distinct from the somatic gonad signal, which is at least partially independent of daf-16, but dependent on the DAF-2 insulin/IGF-1 receptor, as well as daf-9 and daf-12(1,2,3). To further elucidate how the reproductive system controls aging, we performed an RNAi suppressor screen to identify genes required for the longevity of animals lacking a germline (4). This screen of genes on Chromosome I will identify genes that either negatively regulate the germline signal or positively affect the somatic gonad signal. We found 45 RNAi clones that suppress longevity. Of these, 11 clones were isolated that suppress germline-mediated lifespan extension, yet have nominal or no effect on wild-type longevity or apparent health. Several novel genes, including multiple signaling molecules, are among this list of candidates. RNAi of these genes affect daf-2 lifespan in a varying and, in some cases, allele-specific manner. Interestingly, like daf-12 mutations, some of these RNAi clones extend the lifespan of daf-2 mutants. We are continuing epistasis analysis and molecular characterization to further understand the role of these genes in communicating longevity cues from the reproductive system. 1.Hsin and Kenyon, Nature 1999 2.Gerisch et al, Dev Cell 2001 3.JRB and CK, unpublished; A. Antebi, personal communication 4.Fraser et al, Nature 2000